Bug#1095677: lowmem installer UI frames start getting corrupted (UTF-8 as cp437(?)) after first stage of install (@ scanning install media stage)

наб <[email protected]> Mon, 10 Feb 2025 17:51:55 +0100

Newsgroups	gmane.linux.debian.devel.cd
Message-ID	<hl2qfssed2uikmcidt7mif2rfd7gwegbd5utpfg4zlslx2hhh2__11261.6760119394$1739206660$gmane$org@tarta.nabijaczleweli.xyz>

Package: debian-cd
Severity: normal

Hi!

Reported by a friend, I'm reproing in QEMU
(> 4G; truncate -s 4G 4G; qemu-system-x86_64 -enable-kvm -smp 2 -m 500m -cdrom debian-testing-amd64-netinst.iso 4G -bios /usr/share/ovmf/OVMF.fd
 and non-lowmem with -m 2g)
but platform probably irrelevant;
happens on debian-12.5.0-amd64-netinst.iso
           debian-12.9.0-amd64-netinst.iso
           debian-testing-amd64-netinst.iso (dated 2025-02-10 11:30)

Please see attached jpeg.
Repro by just mashing through all the defaults.

This looks like it corresponds to the switch from cp437 box-drawing frames
(M-DM-DM-DM-D) to the thin UTF-8 ones (M-^CM-^TM-^@M-^CM-^TM-^@M-^CM-^TM-^@M-^CM-^TM-^@)
(sorry the d-i busybox doesn't have od, cat -A is the best I could do).

AFAICT, there's no reason for this to happen: all the processes have
LANG=C.UTF-8, which does exist regardless of the mode,
so it's not an incidental bad reinterpretation of UTF-8 box-drawing
characters as bytes in the C locale in some writer process or whatever
(but then I can hardly probe all the incidental processes for LANG[UAGE]/LC_* with /proc/environ;
 pulling in strace confirms C.UTF-8 works).

The VT is -iutf8 by default; stty -F /dev/tty0 -iutf8 and clicking
through for a redraw fixes it,
but non-lowmem doesn't need this to transition properly.

I've exhausted everything I could think of to dissect this outside-in,
the particular mechanics of d-i here are opaque to me.

Best,

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